Abstract：A model based on ideas of thermomechanics，the first and second laws of thermodynamics，is introduced to describe the elasto-plastic behavior of soil deformation，and the method of determining model parameters is provided. Once the forms of the free energy function and dissipation potential function have been specified，the corresponding yield surface，flow rule，hardening rule as well as the elasticity law are deduced in a systematic manner. The plastic work and dissipation energy are distinguished explicitly. Not all plastic work is dissipated，but some are stored and can be recovered under reversed plastic loading. The physical meaning and range of model parameters are discussed. The parameters can be determined by fitting the triaxial test curves，and the genetic algorithm is adopted by using obtained parameters，and a group of drained triaxial tests are computed，and compared with the experimental results to verify the validity of the model. The model automatically satisfies the laws of thermodynamics，and there is no need to invoke any other postulations.
